Recently, in Europe, North America, etc., the use of automobile lights during daytime has been promoted for the purpose of improving visibility from pedestrians and oncoming vehicles in the daytime. A day lamp is usually placed near a head lamp and a rear lamp. For this reason, the structure around lamps is complicated, and it is constructed with members having a fine structure such as a light guide. Moreover, due to the use of automobile lights during daytime, the quantity of heat generated from light sources of lamps is increased, and heat resistance of peripheral members is required. Furthermore, lamps with wide irradiation ranges are desired, and increase in luminance and size of light lenses is desired.
Meanwhile, importance is placed on reduction in weight of automobiles from an environmental perspective. For this reason, it is extremely important to realize reduction in thickness and weight and improvement of impact resistance and strength of not only the above-described lamps, but also exterior and interior members of automobiles.
In general, when producing a large-sized/thin-type molded body by the injection molding method using a thermoplastic resin, it is required to improve the flowability of the resin in order to provide high transferability. For this reason, the viscosity-average molecular weight of the resin is often reduced. However, when the molecular weight of the resin is too small, the strength of the molded body is insufficient and cracking of the molded body is easily caused at the time of mold release. Thus, the improvement of the flowability of the resin by reduction in molecular weight is limited.
Among thermoplastic resins obtained from the same structural unit, there is a tendency that the lower the glass transition temperature (Tg) is, the more excellent the flowability and transferability of a molded body obtained are. However, when Tg is too low, it is impossible to obtain an injection-molded body having excellent heat resistance.
For example, conventional polycarbonate resin obtained by reacting 2,2-bis(4-hydroxyphenyl)propane (common name: bisphenol A, hereinafter abbreviated as BPA) with phosgene or carbonic acid diester (common name: BPA-PC, hereinafter abbreviated as BPA-PC) has excellent heat resistance and transparency and also has excellent mechanical properties such as impact resistance, and therefore is widely utilized not only as a structural material, but also as an optical material for a light guide plate for liquid crystal, an optical disk substrate, various types of lenses, a prism, an optical fiber, etc.
However, recently, with the extension of intended use as optical materials, impact resistance of BPA-PC may be insufficient, and for this reason, it is strongly desired to develop a large-sized/thin-type injection-molded body for vehicles having improved impact resistance.